The present invention relates to encapsulated solar reflecting films for use in laminated window assemblies and more particularly to shatterproof window assemblies having a safety glass type of construction. It further relates to shatterproof laminated window assemblies having high reflection of solar radiation without sacrificing optical properties and defrosting capabilities. The invention finds particular utility in automotive window applications, and in particular for windshield products.
Solar reflecting window assemblies have found application in numerous areas where one objective is to manage internal heat loads by reflecting a portion of the solar spectrum which causes heating, e.g., the near infrared. This technology has been employed, for example, in commercial and residential glazing products and more recently in automotive window products.
The surface areas of automotive windows (front, side and rear) exposed to sunlight have increased in recent years due to the new stylish and aerodynamic vehicle body designs with severely sloping front and rear windows. This increase has resulted in greater heat inside of the vehicles during sunny days and greater frosting, icing and fogging of the windows during the colder days and nights. To reduce the heating effects resulting from such windows, selective light transmitting materials or films have been incorporated into window assemblies. These films have generally been designed to maximize rejection of incoming light in the near infrared wavelength range. Selective light transmitting films are disclosed, for example, in U.S. Pat. Nos. 4,166,876, 4,226,910 and 4,234,654. (The disclosures of these patents and the other patents and applications mentioned herein are hereby incorporated by reference in their entireties.) Electrically-heatable laminated windows to remedy the frosting, icing and fogging problems have been designed and such are disclosed in, for example, U.S. Pat. No. 4,017,661 and pending application Ser. Nos. 07/084,274 and 07/084,600, both filed Aug. 19, 1987, and entitled "Electrically Heatable Laminated Window," of the present assignee.
Further, it is known to provide a safety glass type of construction which is resistant to shatter upon impact by making a laminated window assembly incorporating a flexible plastic safety film (e.g., polyvinyl butyral, PVB) between a pair of glass layers. By including a thin electrically-conductive metal coating in this construction, the safety glass of windshield can also have electrically-powerable defrosting capabilities as previously mentioned. This type of coating is disclosed, for example, in U.S. Pat. Nos. 3,718,535, 3,816,201, 3,962,488 and 4,017,661.
Safety glass type windows, which include the metal layer-containing solar rejection films, reflect heat, control solar radiation, and optionally conduct electricity for defrosting capabilities. Providing such a structure on a commercial scale, however, heretofore has been difficult due to problems associated with lamination, In a typical construction, the solar control film is itself of multilayer design with a number (e.g., three, five, seven or more) of functional coatings on a flexible plastic substrate or carrier layer. This substrate layer, typically polyethylene terephthalate (PET), while transparent, tends to wrinkle during bonding to the safety film (e.g., PVB) and/or lamination of the resulting composite solar/safety film between two additional glass layers using conventional lamination techniques employed for safety glass laminates. These wrinkles, which are particularly noticeable at oblique viewing angles, render the resulting windshield unacceptable because a wrinkled layer in the laminate produces optically non-uniform surfaces which result in distorted reflected images.
One attempt of the prior art to deal with this optical problem is described in U.S. Pat. No. 4,465,736 which uses a solar reflecting coating on a substrate which is heat shrinkable within certain carefully prechosen limits. The major problem with this approach is the potential for unequal thermal shrinkage of the substrate film and the coatings, which an cause the coatings to become discontinuous. discontinuities in the coating can result in degradation of both electrical properties (i.e., higher resistance) and optical properties (i.e., an increase in the scattering of visible light).